Pickling of metal



Aug. 11, 1936 Patented UNITED STATES PATENT OFFICE PICKLING OF METAL NoDrawing. Application September 8, 1935, Serial No. 38,948

13 Claims. (01. 148-8) This invention relates to the acid pickling ofmetal, more particularly to pickling ferrous metals in dilute sulfuricacid solution.

It is among the objects of this invention to provide a method ofpickling and an inhibitor therefor which aflord eflicient pickling andinhibiting, in the use of which satisfactorily uniform inhibiting actionthroughout the use of a given bath is attainable by periodic additionsof inhibitor to the bath, in which uniformity of inhibiting action frombath to bath is readily obtainable. A particular object is to provide aninhibitor which avoids scum formation, is relatively cheap and isaccurately reproducible, is efficient in inhibiting power, and which isnot liable to be decomposed by the heat encountered through the methodscommonly applied for heating pickling baths.

A further object is to provide a method of pre- 0 paring inhibitorsembodying the foregoing characteristics.

I The present invention is predicated upon our discovery that its statedobjects are attained with an inhibitor made by sulfonating an hydroxylic25 organic compound such as a phenol or an alcohol,

a d a mustard oil or a substituted thiogrgg.

examples of the hydroxylic compounds which may be used in the practiceof the invention, we have obtained satisfactory results with 30 suchsubstances as phenol, cresols, especially in the form of crudecreosote,'ethyl alcohol, glycerin, and sulfonated castor 011. As tomustard oils and substitution products of thiourea, we have made highlysatisfactory inhibitors embodying the de- 35 sirable features whichcharacterize this invention from phenyl and diphenyl thiourea, phenylmustard oil, and allyl mustard oil, which are typical of thisconstituent of the reaction mixture. The mustard oils may be said topossess the type for- 40 mula RNCS, in which R may be an alkyl or anaryl group. The substituted thioureas may be said to possess the typeformula in which R and R1 are amino or substituted amino groups.Compounds of the latter type yield products of the former type upontreatment with con- 50 centrated sulfuric acid.

In the practice of the invention the materials designated are subjectedto sulfonation, for example by mixing them with 60 to 66 B. sulfuricacid. while w'do not understand exactly what 55 reaction occurs, we nowbelieve that the constituents react to produce a new chemical identitywhich then undergoes sulfonation. We do not, of course, limit ourselvesto that theory, and whatever be the nature of the change which occurs,such products provide unusually efficient 5 and desirable picklinginhibitors. For instance, very low concentrations of the inhibitorsprovided by this invention suiiice to afford satisfactory inhibition,and the inhibitors appear to be comparatively stable to the variousactions 10 which may, and in many instances do, cause deterioration ofthe inhibitors used previously.

The inhibitors provided by this invention do not cause scum, and for themost part they are relatively cheap to make, and pickling costs are low1 in any event because of the very low concentrations of inhibitorswhich suffice to provide satisfactory pickling conditions. In addition,the inhibitors of this invention represent materials of rather definitecharacter and they are readily reproducible, and it is thereforepossible to attain uniformity of pickling action from bath to bath.Another desirable feature is that by periodic additions of the inhibitorto the bath, as need be, uniform pickling action is achieved, a resultnot always attainable with other inhibitors.

The proportions in which the inhibitor-forming constituents are usedwill depend, as will be understood, upon the particular hydroxyllccompound and mustard oil, or substituted thiourea, used. By way ofillustration, however, satisfactory results have been had using theproportions of 1 mol. of thiocarbanilide to 2 mols. of ethyl alcohol,phenol, or cresol. When using creosote we have found it fullysatisfactory in calculating amounts to be used to consider it as beingpure cresol. Likewise, we have had satisfactory results using one-fifthmol. of sulfonated castor oil per mol. of phenyl mustard oil or ofthiocarbanilide. The proportions may, of course, be varied from thosejust stated.

The invention also provides a convenient method of preparing theinhibitors in an unusally effective and desirable form. In accordancewith so controlled that the temperature does not become excessive, andusually it is desirable to keep the temperature below about 100 F. In

separate container the remaining portion of 6 the hydroxylic compound ismixed with the mustard oil or substituted thiourea to form a thin I astewhich is then added to the acid reaction ture just described, the sameconditions being observed. When all of the pasty material has 1 beenadded the preparation of the inhibitor is complete.

This method is readily controlled, can be carried out in simple andinexpensive apparatus, and it provides the inhibitor in a liquid formwhich 15 is readily handled and can be measured easily for proper dosageof the pickling bath.

In the practice of the invention the inhibitor is added to a solution ofstrong "1 for pickling errous metals. Low concentrations of theinhibitors provided by this invention sufiice, and our work has shownthat for pickling both low and high carbon steels in an 8 percentsolution of sulfuric acid at tempera- 25 tures up to 180 F., aconcentration of about 0.04

'per cent is satisfactory. Most suitably the ino the con p or to rm n|pickling ferrous metal articles.

As illustrative of the benefits to be derived from the invention,reference may be made to tests showing the eilicacy of these inhibitors.In these tests the pickling bath comprised 230 cc. of a utility for g 357.6 per cent solution of sulfuric acid at a temperature of 150 F. Theinhibitors listed in the following table were prepared in accordancewith the method justdetailed; 0.1 cc. of the inhibitor was added tothe"pickle bath. The material 40 pickled was cold rolled, low carbonstrip about 0.005 inch thick made from a steel containing about 0.1 percent of carbon; the strip was cut to form rectangles 3 x 1.5 inches. Thesamples were preliminarily cleaned, dried, and weighed. 45 Afterimmersion for 30 minutes in the pickling bath they were again cleanedand\dried, and the weight loss was determined. For comparison identicaltests were made using an identical pickling bath without inhibitor, andalso iden- 50 tical baths containing a well-known commercially usedinhibitor. The results were: as follows:

Average weight Comparable results were obtained also with 65 high carbonsteel.

From the foregoing tests it appears clearly that the inhibitors providedby the present invention very substantially reduce the action of thepickling bath on the metal, and that the weight loss 70 is approximatelyhalf that obtained with the commercial inhibitors referred to.

The use of higher concentrations of these inhibitors than those used inthe tests, for instance in amounts of 1 cc. per 230 cc. of picklingsolu- 75 tion, appears to have no material effect in improving theinhibiting action, showing that very small amounts indeed sumce for manypurposes.

Without restricting ourselves, we now believe that in the production ofthese inhibitors there occurs a reaction by which there is formed a sub-5 stance of the following type formula in which R, R1, and B: may be ahydrogen, an

alkyl, an aryl, or a substituted aryl group. We now believe, although wedo not limit ourselves to this theory, that hen substituted thloureasare used in thanractice o 'thifivenon 1 by thfin ulfonating medium withfdrma'tiUlTUTT such as phenyl' case of arbanilide, and that it is thatmustard oil which is e ac.t ive c ns 1 W compound, in r nnibitcTrT(recording to the provisions of the patent statutes, we have explainedthe principle of our invention, and have described what we now considerto be its best embodiment. However, we desire to have it understoodthat, within the scope of the appended claims, the invention may bepracticed otherwise than as specifically described.

We claim:

1. That method of pickling metal in a strong mineral acid bathcomprising subjecting said metal to a bath of said acid containing asmall amount of a product obtained by sulfonating a mixture of anorganic hydroxylic compound and a substance of the group mustard oilsand substituted thioureas.

2. That method of pickling metal in a strong mineral acid bathcomprising subjecting said metal to a bath of said acid containing asmall amount of a product obtained by sulfonating a mixture of asubstance of the group phenols and alcohols, and a substance of thegroup mustard oils and substituted thioureas.

3. That method of pickling metal in a strong mineral acid bathcomprising subjecting said metal to a bath of said acid containing asmall amount of a product obtained by sulfonating a mixture of asubstance of the group phenols and alcohols, and a substance of thegroup mustard oils and organic compounds producing mustard oils in thepresence of strong sulfuric acid.

4. That method of pickling ferrous metal comprising subiecting saidmetal to a bath of dilute sulfuric acid containing a small amount of aproduct obtained by sulfonating a mixture of a substance of the groupphenols and alcohols, and a substance of the group mustard oils andsubstituted thioureas.

5. That method of pickling ferrous metal comprising subjecting saidmetal to a bath of about 8 per cent sulfuric acid heated to about 150 F.and containing a small amount of a product obtained by sulfonating amixture of a compound of the group phenols and alcohols, and a substanceof the group mustard oils and substituted thioureas.

6. That method of pickling metal in a strong mineral acid bathcomprising subjecting said metal to a bath of said acid containing asmall amount of a product obtained by sulfonating a mixture of ethylalcohol and a mustard oil or a substance producing mustard oil in thepresence of strong sulfuric acid.

'1. That method of pickling metal in a strong 75 252. COMPOSITIONS,

mineral acid bath comprising subjecting said metal to a bath of saidacid containing a small amount of a product obtained by sulfonating amixture of phenol and a mustard oil or a substance producing a mustardoil in the presence of strong sulfuric acid.

8. That method of pickling metal in a strong mineral acid bathcomprising subjecting said metal to said bath containing a small amountof a product obtained by sulfonating a mixture of (1) an organichydroxyl compound of the group phenol, cresol, creosote, glycerin, andsulfonated castor oil, and (2) a substance of the group phenyl thiourea,diphenyl thiourea, phenyl mustard oil and allyi mustard oil.

9. That method of pickling ferrous metal in a bath of dilute sulfuricacid, comprising subjecting said metal to said bath containing a smallamount of a product obtained by sulfonating a mixture of (1) an organichydroxyl compound of the group phenol, cresol, glycerin, and sulfonatedcastor oil, and (2) a substance of the group phenyl thiourea, diphenylthiourea, phenyl mustard oil and allyl mustard oil.

10. That method of pickling ferrous metal comprising subjecting saidmetal to a bath of about 8 per cent of sulfuric acid containing a smallamount of a product obtained by sulfonating a mixture of (1) an organichydroxyl compound of the group phenol, cresol, glycerin, and sulfonatedcastor oil, and (2) a substance of the group phenyl thiourea, diphenylthiourea, phenyl mustard oil and aliyl mustard oil.

11. That method of pickling metal in a strong mineral acid comprisingsubjecting said metal to an acid pickling bath containing a small amountof a product obtained by sulfonating a mixture of an organic hydroxylcompound and a compound of the type formula cs 1 in which R and R1 areamino or substituted amino groups.

12. That method of pickling ferrous metal comprising subjecting saidmetal to a dilute bath of sulfuric acid containing a small amount of aproduct obtained by sulfonating a mixture of an organic hydroxylcompound and a compound of the type formula in which R, R1, and R2 maybe hydrogen, an alkyl group, an gr yl group or a substituted aryl group.

CHARLES H. MCCOLLAM. DWIGHT L. WARRICK. JOHN M. GOTSHALL.

